Deadly Hydrogen Sulfide Accident Puts Deer Park in Headlines Again

 

A friend once summarized much of engineering ethics to me in two words:  "No headlines."  If that's a good guideline for engineering ethics, the city of Deer Park has seen two major violations of it in less than a month. 

 

Following a giant pipeline fire that burned for four days in September, on last Thursday, Oct. 10, some contract employees at the PEMEX refinery in Deer Park were working on a pipe flange, and something went wrong, releasing the pipe's contents into the air.  They may or may not have known that the pipe was carrying hydrogen sulfide (H₂S), which is a byproduct of oil refining.  It is probably familiar to most readers as the "rotten egg" odor that comes from aged chicken products and sewer gas.  The human nose can detect it at concentrations as low as one part per billion.  Unfortunately, one of its toxic effects is to deaden the olfactory nerves, causing the perceived smell to go away and leading to a false sense of security as concentrations increase.  It is highly toxic, and concentrations as low as 100 parts per million are classified as "immediately dangerous to life and health."

 

Two contract workers died in the accident, which occurred around 4:40 in the afternoon, and 35 others were exposed to the gas to the extent of needing treatment.  The bodies were not recovered until 3:30 AM the next day after the area had been cleared of toxic gas.

 

The city of Deer Park sent out shelter-in-place orders to its residents around 6:30 PM, but due to technical difficulties with the alert system, some people were not alerted until they read about the incident on social media.  A supplemental siren system in the city is due for an upgrade soon.

 

The accident is under investigation by both local authorities and the U. S. Chemical Safety and Hazard Investigation Board, but no cause has yet been determined. 

 

As we noted two weeks ago when writing about the pipeline fire, residents of Deer Park and surrounding communities in Houston are no strangers to refinery-related emergencies.  Release of toxic chemicals in oil refineries has been happening ever since there were refineries, and the industry has adapted to steadily increasing standards for air and water pollution control and safety measures over the decades.  The PEMEX refinery where this accident occurred dates back to 1929, when it was built by Shell Oil.  In 1993, Shell sold half the facility to the Mexican national petroleum company PEMEX and operated it as a joint venture until 2022, at which point Shell sold its share and PEMEX became the sole owner and operator.  This change of ownership may or may not have anything to do with the accident, but management cultures can change with ownership changes, and the upcoming investigation may answer that question as well as many others.

 

Considering the extremes of temperature and pressure under which highly flammable and toxic chemicals are processed in refineries, it's a wonder that we don't have a refinery explosion every day.  But it's the job of engineers to make sure that every possible thing that can go wrong in a refinery is anticipated and forestalled, and far more than 99.9% of the time, this foresight prevents mishaps. 

 

As with airline accidents, by far the most frequent cause of chemical-plant accidents is human error rather than a simple failure of machinery, although the two can be mixed.  The accident in question could have happened because the workers involved misidentified a flange to be worked on.  An oil refinery is one of the most complicated pieces of plumbing on earth, with thousands of valves, flanges, pipes, processing units, and interconnections.  Refinery workers have to know exactly what they are dealing with before taking any action that could conceivably release a product, and it might have been a case of simply opening the wrong flange.  Or an operator may have believed that the pipe in question had been purged of H₂S when in fact it hadn't been.  You can't tell the contents of a steel pipe just by looking, so there must be elaborate protocols in place to verify what is where, especially when maintenance operations are in progress. 

 

It is incidents like this one which make refineries and petrochemical plants high on the NIMBY list—"not in my back yard."  Given that a country wants to have fossil-fuel products, and given that it has considerable expertise and resources to make them, we in the U. S. must have refineries somewhere.  According to a list of new refineries compiled by the U. S. Energy Information Agency, the U. S. refining industry has managed to add considerable refining capacity since 2014 by building new refineries, but they tend to be in or near existing ones—Houston, Corpus Christi, or various locations in Alaska.  It's a lot easier to upgrade an existing refinery or build a new one next to an existing one, than it is to install the infrastructure of pipelines and shipping facilities in a place without refineries at all.

 

For the foreseeable future, the global economy will rely on fossil fuels, and so we will have to put up with refineries and everything that goes with them.  But people who live near them and work in them have a right to expect that they will be operated as safely as human ingenuity can manage. 

 

That was obviously not the case at the PEMEX plant last week.  We will follow this accident in the future, and when the investigation concludes, perhaps we will learn what chain of events led to an accident that killed two people and endangered an entire community.  But until then, we can take some comfort in the fact that refineries rarely show up in headlines, despite all the dangerous stuff going on in them.

 

Sources:  I referred to articles on the H₂S accident by ABC News 13 in Houston at https://abc13.com/post/pemex-chemical-leak-crews-waiting-lower-levels-before-entering-unit-center-deadly-hydrogen-sulfide-deer-park/15416337/, an article in the Saturday Oct. 12 edition of the Austin American-Statesman, "2 dead, dozens of others injured in hydrogen sulfide leak near Houston," and the Wikipedia article on PEMEX Deer Park.  The Energy Information Agency data is from https://www.eia.gov/tools/faqs/faq.php.

Do You Smell Gas? Thank New London

On Thursday, March 18, 1937, a seventh-grade girl named Sibyl sat in a school bus outside the junior-senior high school building built four years earlier in the unincorporated town of New London, Texas.  In contrast to the rest of the nation, New London and the surrounding area of East Texas were prospering from a local oil boom, and many of the school's students came from families drawn to the area by oil-field jobs.  Sibyl had mistakenly left her class early, but rather than go back inside and look foolish, she had decided just to wait in the bus until school let out for the day in another twenty minutes or so.  Suddenly, at 3:17 PM, she saw the entire front of the building rise several feet into the air and then collapse into a huge pile of dust with a thunderous crash.  She had just narrowly escaped what turned out to be the worst school disaster in the history of the United States.  Over three hundred children and adults died either in the explosion itself or as a result of injuries they sustained in it.  The cause?  Odorless natural gas.

As you may know, natural gas has no characteristic odor of its own.  By law, a malodorant must be added to natural gas for non-industrial users such as homes, businesses, and schools so that a leak will call attention to itself by means of smell.  One of the compounds used, butyl mercaptan, is so stinky that the average human nose detects it at a level of 0.33 parts per billion.  That concentration amounts to one teaspoon of malodorant in a cube of air about 25 meters (80 feet) on a side.  While gas leaks and explosions still occur, the chances of detecting a leak before it causes an explosion are much better when the gas contains a malodorant. 

Flammable gas has been used for domestic light and heat since the early 1800s, but until the discovery of large supplies of natural gas, piped-in gas was a relatively costly type of utility that was confined to cities.  By contrast, the oil wells around New London freely produced so much natural gas that it was (and still often is) considered a waste product, and was flared off near wells in towering flames that burned day and night and could be seen for miles.  The oil companies piped some of it around in what were called bleed-off lines to supply power for their own operations, and because many of New London's residents were already familiar with oilfield equipment and piping, tapping a nearby gas line for free raw natural gas became a common practice.  Although it was technically illegal, someone with the requisite skills could install his own private gas line to an oil lease's bleed-off line, and enjoy free gas instead of paying the local gas utility for it. 

It is a matter of record that a couple of months before the 1937 explosion, W. C. Shaw, superintendent of the New London schools, authorized a janitor to disconnect the schoolhouse from the local gas utility and tap a nearby bleed-off line instead.  Mr. Shaw apparently viewed this as a cost-saving measure, similar to the earlier decision when the school was built to forego the usual steam-boiler-radiator heating system, and instead install an extensive gas piping system and some seventy gas space heaters instead. 

In My Boys and Girls Are in There, a recent book on the tragedy, historian Ron Rozelle notes that many subsequent summaries of the disaster tend to blame Superintendent Shaw for endangering the lives of his charges with the decision to use free untreated bleed-off gas.  The critical question, which Mr. Rozelle doesn't answer in the book, is whether the local gas company was adding malodorant to its product at the time.  Such a practice was widespread by 1937, but by no means universal.  If the utility's gas was odorless as well, then the decision to switch to bleed-off gas made no difference, because the leak that caused the explosion would not have been any easier to detect.  The main reason that the explosion was so severe and extensive was that the poured-concrete school building had a single, poorly ventilated, and uninterrupted crawl space beneath the entire front part of the building, under eight inches of solid concrete floor.  Since natural gas (primarily methane) is lighter than air, this crawl space formed a good container for thousands of cubic feet of gas, which was touched off on that fatal day when a shop teacher switched on an electric sander in the basement. 

While the New London explosion dominated national news for a week or so, it faded quickly as other events diverted the public's attention.  Like war veterans often do, survivors of the explosion usually refused to talk about it afterwards.  However, one survivor, fifth-grader Carolyn Jones, had the courage to make a speech to the Texas House and Senate in Austin only a week after the explosion, urging that safety measures be passed to prevent another disaster like the one at New London.  The result?  Two laws:  one requiring all natural gas for domestic purposes to contain a malodorant, and the other requiring that anyone working on residential natural-gas lines for residential use must be trained and certified for such work by the state of Texas.  The publicity of the New London disaster furnished ammunition for the passage of similar laws in other states, so that eventually, all natural gas sold for household use would carry its own portable detection system, namely, a bad smell.

The New London explosion and its aftermath form a familiar pattern:  first an innovation (the use of natural gas for domestic gas supplies was fairly new in the 1930s); then a tragedy resulting from inadequate safeguards, ignorance, or other factors; then regulations, or a change in good engineering practices, or both, all inspired by the tragedy.  It would be nice if engineers were able to anticipate everything that could go wrong in a novel situation.  But human ingenuity being both fallible and limited, sometimes we have to learn from mistakes, and the more costly the mistake in terms of lives, the faster we learn.  While nothing will ever bring back those three hundred lives lost on that East Texas afternoon seventy-six years ago, it is some comfort to know that their lives were not lost in vain, and that gas users around the globe are safer as a result. 

Sources:  I thank Andrea Nelson and Stephen Paul for bringing my attention to Ron Rozelle's book My Boys and Girls Are in There (College Station:  Texas A&M University Press, 2012), which I relied on for most of the material in today's column.  I also referred to the Wikipedia articles on the history of manufactured gas, thiols, and tert-butylthiol.